Carrier Aero 39MN Series Installation, Start-Up And Service Instructions Manual page 180

WARNING
The use and storage of gasoline or other flammable vapors
and liquids in open containers in the vicinity of this appli-
ance is hazardous and may result in fire or explosion.
Also, note the following points:
• The duct furnace(s) or rack system furnaces do not have
a pilot. They are equipped with a direct spark ignition
device that automatically lights the gas burner. Do not try
to light burners by hand.
• Before operating, leak test all gas piping up to heater gas
valve. See the section Gas Supply, Piping, and Connec-
tions on page 167 (duct furnaces) or page page 172 (rack
system furnaces). Smell around the unit area for gas. Do
not attempt to place heater in operation until source of
gas leak is identified and corrected.
• Do not attempt to operate unit if there is any indication
that any part or control has been underwater. Any control
or component that has been under water must be replaced
prior to attempting to start the unit.
• Use only hand force to push and turn the gas control
knob to the "ON" position. Never use tools. If knob does
not operate by hand, replace the gas valve before starting
the unit.
WARNING
If the gas control knob does not operate by hand, replace it
before starting the unit. Forcing or attempting to repair the
gas valve may result in fire or explosion.
Start-Up (Duct Furnace) — Follow these steps to start the
gas-fired duct furnace:
1. Turn thermostat or temperature controller to its lowest
setting.
2. Turn off gas supply at the manual shut-off valve.
3. Turn off power to the unit at the disconnect switch.
4. Remove access panel or open door to unit vestibule hous-
ing the gas heater.
5. Move gas control knob to "OFF" position.
6. Install a tapped fitting for attachment to a manometer, or
other gage suitable for 14.0 in. wg in the inlet pressure
tap, and for 10.0 in. wg in the manifold pressure tap.
7. Wait 5 minutes for any gas to clear out. If you smell gas,
see Step 2 and correct leak. If there is no odor or leaks
have been corrected, go to the next step.
8. Turn gas control knob to "ON" position.
9. Open all manual gas valves.
10. Turn power on at disconnect switch.
11. Set thermostat or controller to its highest position to initi-
ate call for heat and maintain operation of unit.
The draft inducer will run for a 15 to 30-second pre-purge
period. At the end of the pre-purge period, the direct spark will
be energized and the gas valve will open. The burners ignite.
Failure to Ignite (Duct Furnace) — On the initial start-up, or
after the unit has been off for long periods of time, the first
ignition trial may be unsuccessful due to the need to purge air
from the manifold at start-up. If ignition does not occur on the
first trial, the gas and spark are shut off by the ignition control
and the control enters an inter-purge period of 15 seconds,
during which the draft inducer continues to run. At the end of
the inter-purge period, another trial for ignition will be initi-
ated.
Control will initiate up to three ignition trials on a call for
heat before lockout of control occurs. Control can be brought
out of lockout by turning thermostat or controller to its lowest
position, waiting 5 seconds, and then turning back up to call for
heat. Controls will automatically reset after one hour and initi-
ate a call for heat.
Manifold Pressure Adjustment (Duct and Rack System Fur-
naces) — A pressure tap is provided in each furnace manifold
for measuring the gas manifold pressure. Manifold pressure
must be checked at start-up and during any service or mainte-
nance. All control systems require a manifold pressure of 3.40
to 3.50 in. wg at maximum input rating on natural gas, and
10.0 in. wg on propane gas at maximum input rating. See Fig.
142-144 on page 169 for gas valve adjustment locations.
NOTE: For two-stage and modulating control applications,
verify proper low fire adjustments as outlined in the Sequence
of Operation document provided in the instruction package.
Check the furnace section for this document or contact your
Carrier service representative.
Burner Flames (Duct and Rack System Furnaces)
Before completing the start-up, check the appearance of the
main burner flame.
1. The burner flame should be predominately blue in color,
and well-defined and centered at the tube entry as shown
in Fig. 159. Distorted flame or yellow tipping of natural
gas flame, or a long yellow flame on propane, may be
caused by lint and dirt accumulation inside burner or at
burner ports, at air inlet between burner and manifold
pipe, or debris in the main burner orifice. Soft brush or
vacuum clean affected areas.
2. Poorly defined, unfocused, substantially yellow flames,
or flames that appear weak or wavering, indicate poor air
supply to burners or excessive burner input. Verify gas
supply type and manifold pressure with rating plate.
Poor air supply can be caused by obstructions or blockage
in heat exchanger tubes or vent discharge pipe. Inspect and
clean as necessary to eliminate blockage. Vacuum any dirt or
loose debris. Clean heat exchanger tubes with stiff brush.
Poor flame characteristics can also be caused by undersized
combustion air openings or flue gas recirculation into combus-
tion air supply. Increase air opening size or re-direct flue prod-
ucts to prevent re-circulation.
Reduced air delivery can also be the result of fan blade slip-
page, dirt accumulation on the fan blade, or low voltage to draft
inducer motor. Inspect draft fan assembly and be sure fan blade
is secure to motor shaft. Check line voltage to heater.
Fig. 159 — Proper Flame Appearance
Normal Operation (Duct and Rack System Furnaces)
1. Turn on electrical supply to unit at disconnect switch.
2. Turn on manual gas supply.
3. Set thermostat or temperature controller to desired tem-
perature.
Information outlining the normal sequence of operation and
wiring diagram for the control system supplied with the fur-
nace model is located in the furnace section, or contact your
Carrier service representative.
Shutdown (Duct and Rack System Furnaces)
1. Set thermostat or controller to lowest setting.
180
—
A48-